Medical implantable lead with fixation detection

ABSTRACT

A lead has a helix at a distal end of a rotatable shaft. Prior to implantation of the lead, the helix has a first configuration comprising an electrically active surface coated with an electrically insulative layer of a biologically dissolvable material to render the helix electrically inactive. Upon fixation of the helix into an organ, the helix has the first configuration and a pin is in electrical contact with the organ to detect proper fixation of the helix into the organ. Subsequent to fixation of the helix into the organ, the helix has a second configuration comprising an electrically active surface exposed upon dissolving of the electrically insulative layer of the biologically dissolvable material to render the helix electrically active.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.13/509,530, filed May 11, 2012, which is a 371 of InternationalApplication No. PCT/SE09/051356, filed Nov. 30, 2009.

FIELD OF THE INVENTION

The present invention relates to a medical implantable lead of the kindbeing adapted to be implanted into a human or animal body for monitoringand/or controlling of an organ inside the body, comprising in a distalend a tubular header inside which a shaft is rotatable as well asextendable and retractable arranged and carries in a distal end acombined fixation means and electrode member in form of a helix, whichis provided with a first contact surface being electrically connectibleto a connector at the proximal end of the lead by means of an electricconductor, and which by means of the shaft is rotatable in relation tothe lead and extendable out from the distal end to be able to fixate thedistal end of the lead to the organ by being screwed into the tissue,wherein the shaft also is provided with a second contact surface beingpositioned on or adjacent a proximal portion of the helix which islocated beyond the distal end of the shaft and being connectible to aconnector at the proximal end of the lead by means of an electricconductor.

BACKGROUND OF THE INVENTION

Implantable medical leads having a helix, which is rotatable as well asextendable out from and retractable into a tubular header in the distalend of the lead, and which functions both as a fixation means, forattaching to the tissue of an organ inside a body, and an electrodemember for transmitting and/or receiving electrical signals to and fromthe organ, are well known in prior art. Such medical implantable leadsare e.g. used to connect a pacemaker or a cardiac defibrillator deviceto a heart, but also other applications for monitoring and/orcontrolling the function of other organs could be conceivable with sucha lead.

Normally, such a medical implantable lead is implanted from the outsideof the body. For example in case of a pacemaker, the lead can beintroduced into a heart through a vein and attached to the inner surfaceof a heart wall. The physician performing the implantation cannotactually see when the implantation is performed other than by means ofx-ray imaging and accordingly it is hard to verify the performance ofthe attachment.

It can be extremely important for a patient that the fixation of thehelix is done properly, both in relation to transmitting of electricalsignals between the tissue and the helix as well as in relation to longterm secure attachment of the lead to the organ such that the lead isnot accidently disengaged from the organ. Poor helix fixation is a wellknown problem and till now there has been no good way of verifyingwhether a helix is properly secured to the tissue or not. In prior artit has been known to e.g. perform current of injury measurements, i.e.to measure the potential difference between injured tissue, e.g. tissuewhich is penetrated by a helix, and uninjured tissue, or to performmechanical pull tests of the attached lead. Both of these methods areassociated with drawbacks since they can appear to indicate a properfixation even when only a small part of the helix actually is secured tothe tissue. Also, by manufacturing the header and the helix of aradiopaque material it is, by means of x-ray imaging, possible to seewhen a helix is sufficient screwed out from the header by counting thenumber of wire loops that is visible beyond the distal end of theheader. However, by this method it is not possible to see whether thesewire loops are embedded into tissue or not, since the tissue itself isnot visible on the images. Another way of ensuring that the helix issufficient screwed out from the header is to count the number of turnsthe physician is rotating a helix rotating control member whenperforming the screwing out of the helix from the proximal end. Due tooccurring elastic properties in a rotatable torque transferring member,usually a rotatable wire coil, extending from the helix rotating controlmember to the shaft, and friction between the torque transferring memberand the rest of the surrounding lead, it is however necessary to rotatethe helix rotating control member more than the theoretically requirednumber of turns to be sure that the helix will be sufficient screwedout. This result in a risk that the helix my become completely screwedout while the physician continuous to rotate the helix rotating controlmember such that the distal end of the whole lead is twisted and mayperforate e.g. a heart wall.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a medical implantable lead,according to the introductory part, by means of which it is possible todetect whether the helix is sufficient screwed into and embedded intissue or not. At least this object is achieved by a medical implantablelead according to claim 1.

Accordingly, the basis of the invention is the insight that this objectmay be achieved by providing the helix or the shaft, in addition to afirst contact surface on the helix, with also a second contact surfacebeing located sufficient far in the proximal direction of the lead fromthe distal tip of the helix and more precisely in or adjacent a proximalportion of the helix which is located beyond a distal end of the shaft.Moreover, the first contact surface on the helix is electricallyinactive at least during an initial stage during implantation of thelead in the body.

Within this overall idea, the invention may be varied and modified inmany different ways within the scope of the invention. An importantfeature of the invention is that the second contact surface has to beprovided, permanently or temporarily, on the helix or on the shaft or onsome other member which is moved together with the shaft and the helixduring rotation and extending of the helix when implanting the lead intothe body. Moreover, the second contact surface has to be positioned onor at a proximal portion of the helix, more precisely on or at a portionfrom the distal end of the shaft to half the length of the helix,preferably from the distal end of the shaft to 25% of the length of thehelix and most preferred from the distal end of the shaft to 10% of thelength of the helix. Accordingly, the second contact surface cannot bearranged on for example the distal end surface of the header since thatsurface may come into contact with the tissue even though the helix isnot completely screwed out from the header. Also, it is to be understoodthat in case of a unipolar lead, these first and second contact surfaceswill be sufficient. However, in addition to the first and second contactsurfaces, the lead can also be provided with one more electrode surfacein case of a bipolar lead, two or more electrode surfaces in case of atripolar lead, etc.

In one embodiment of the invention, a first contact surface at a distalportion of the helix is initially inactivated by being coated with anelectrically insulating layer of a biologically dissolvable substance,and hence not electrically conducting, while a second contact surface ata proximal portion of the helix is active, and hence electricallyconducting, by being free from any electrical insulation. Whenimplanting the lead, it is possible to detect, by electric measurements,if the helix is so far screwed into the tissue such that the secondcontact surface at the proximal portion of the helix is in contact withthe tissue or not. After having been embedded a while in the tissue, thetime being determined by the specific biological dissolvable materialbeing used and the thickness of the layer, the insulation layer on thedistal portion of the helix will begin to dissolve and vanish such thatalso the distal portion of the helix will gradually begin to beelectrically conducting. In this embodiment it is not necessary toseparate the first and second contact surfaces on the helix by welldefined limits. Instead they may represent one and the same continuouselectrode surface of which a distal portion, i.e. which represents thefirst contact surface, is coated with an electrically insulating layerof a biologically dissolvable material, while a proximal portion, whichrepresents the second contact surface, is free from any electricallyinsulating layer.

In an alternative embodiment at least the entire part of the helix whichprotrudes beyond the distal end of the header in the screwed outcondition of the helix, is coated with an electrically insulating layerof a biologically dissolvable material. The second contact surface, onthe other hand, is arranged on or carried elsewhere on the rotatable andextendible shaft which also carries the helix. Such a contact surfacecan be formed as a separate contact member protruding from the shaft orjust constitute the whole or a part of the end surface of the shaft. Inthe former case the contact member usually is formed for and adapted topenetrate into the tissue when implanting the lead, and for this reasonit is important that it is coaxially arranged in relation to the helixbecause otherwise the contact member will tear up a wound in the tissuewhen rotating the shaft and the helix. In the latter case the contactsurface will have the function of a contact surface adapted to transmitsignals by abutment against the surface of the tissue and for thisreason it is not critical that the contact surface is coaxially arrangedin relation to the helix even though this is preferred. Neither of theseembodiments requires that the first and second contact surfaces are partof different electric circuits.

In yet another embodiment, the first and second contact surfaces areelectrically insulated in relation to each other and are part ofdifferent electric circuits. One way of accomplish this is to connectthe first and second contact surfaces to an electric connector in theproximal end via a common electric conductor and arrange an electricswitch close to the distal end of the lead, preferably at the proximalend of the header. By means of the switch it is possible to choose whichone of the first or second contact surfaces that should be connected tothe connector in the proximal end of the lead. Accordingly, it isnecessary to connect the first and second contact surfaces,respectively, to the switch by means of separate electric conductorswhich are electrically insulated in relation to each other and also thefirst and second contact surfaces have to be electrically insulated inrelation to each other. However, the first contact surface does not haveto be coated by an electrically insulating layer of a biologicallydissolvable material, as in the previous embodiments. The switch can beof an electrically operable type, for example as is disclosed in U.S.Pat. No. 5,423,873 or U.S. 2008/0294218 A1, or be of a mechanicallyoperable type which e.g. is shifted by means of a stylet or the likewhich is introduced through a tubular bore arranged axially in thecenter of the lead. The stylet may optionally shift the switch by e.g. arotational or a pushing movement. By means of a medical implantable leadarranged in this way, it is possible for a physician to repeatedlyswitch between a fixation confirmation state, when the second contactsurface is connected to the connector in the proximal end, and anoperating state, when the first contact surface is connected to theconnector in the proximal end.

Also in a further embodiment, the first and second contact surfaces areelectrically insulated in relation to each other and are part ofdifferent electric circuits. However, in this embodiment the first andsecond contact surfaces are also connected to the proximal end of thelead by means of different conductors. The conductor to the secondcontact surface can be a permanent conductor, e.g. in form of oneadditional electric wire in a wire coil extending from the header to theproximal end and connected to a separate connector surface in theproximal end. However, the conductor to the second contact surface couldalso be a temporary conductor, e.g. an electrically conducting styletwhich is temporarily introduced into the axially center bore in the leadand which is utilized to perform measurements during implantation stage,for confirmation that the helix is screwed sufficient deep into thetissue, and subsequently is removed.

In a still further embodiment, the lead is provided with a continuousthrough bore from the proximal to the distal end, i.e. also through theshaft, such that a temporary conductor in form of a stylet is insertablethrough the bore for contact with or penetration into the tissue.Accordingly, in this embodiment the stylet will function not only as aconductor, but also its distal end will function as the second contactsurface and its proximal end will function as a connector to beconnected to a measuring device. In order to prevent too deeppenetration into the tissue, the stylet should be provided with somekind of stop member, which can engage with a mating stop member of thelead. In the hereinafter illustrated and described embodiment, the stopmember on the stylet is in form of a shoulder portion near its distalend which engages a corresponding shoulder portion inside the bore.However, the stop members could be formed in many different ways, e.g.as a pin on the stylet, and be positioned also at other locations, e.g.in its proximal end. To prevent electric contact with conductors withinthe bore or with the shaft, the stylet could be provided with anelectrically insulating layer except in its distal end, which is adaptedto function as the second contact surface, and in its proximal end,which is adapted to function as a connector. The stylet could preferablybe formed of or comprise a radiopaque material to visually be able todetermine whether it is correct positioned or not.

It is to be understood that the electric measuring of whether the secondcontact surface is electric contact with the tissue or not, can becarried out in different ways and by means of different equipment. Incase of a medical implantable lead connected to a heart, it is possibleto use a so called Pacing System Analyzer (PSA) and, via the secondcontact surface, detect a sufficient R-wave amplitude which wouldindicate a proper contact with the tissue. Using the PSA it is alsopossible to send out pace pulses that would enter the heart muscle viathe second contact surface and a proper voltage capture level willindicate a secure helix engagement to the heart tissue. When using apenetrating member, such as a pin or a stylet, as a second contactsurface, it would also be possible to detect a current of injury signalfrom the injured cells in the tissue, which would indicate a properattached helix.

The invention will hereinafter be explained with reference to a medicalimplantable lead adapted to be attached in its distal end to the tissuewithin a heart and connected to a pacemaker or a cardiac defibrillatordevice in its proximal end. However, as mentioned hereinbefore, alsoother types of medical implantable leads for other purposes andconnected to other organs within a human or animal body, could beconceivable. It is also to be understood that the embodiments are onlyexamples and that the invention could be varied and modified in alsomany other ways within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Different embodiments of the invention will hereinafter be described indetail with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a medical implantable lead with thehelix in an extended state in the distal end;

FIG. 2 is a perspective view of the distal end of the lead in FIG. 1with the helix in a retracted state;

FIG. 3 is a longitudinal section through a distal end of a medicalimplantable lead according to a first embodiment, with the helix in aretracted state;

FIG. 4 is a longitudinal section according to FIG. 3 with the helix in acompletely extended state, however incompletely screwed into the tissue;

FIG. 5 is a longitudinal section according to FIGS. 3 and 4 with thehelix in a completely extended state as well as completely screwed intothe tissue;

FIG. 6 is a perspective view of the distal end of the lead according toFIGS. 3-5 with the helix in a completely extended state;

FIG. 7 is a longitudinal section through a distal end of a leadaccording to a second embodiment;

FIG. 8 is a longitudinal section through a distal end of a leadaccording to a third embodiment;

FIG. 9 is a longitudinal section through a distal end of a leadaccording to a fourth embodiment;

FIG. 10 is a longitudinal section through a distal end of a leadaccording to a fifth embodiment;

FIG. 11 is an enlarged longitudinal section of a mechanical switch inthe embodiment according to FIG. 10;

FIG. 12 is a longitudinal section through a distal end of a leadaccording to a sixth embodiment;

FIG. 13 is a longitudinal section through a distal end of a leadaccording to a seventh embodiment; and

FIG. 14 is a longitudinal section through a distal end of a shaftaccording to an eighth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates in a perspective view, the exterior appearance of anexemplary medical implantable lead according to the invention. The leadcomprises in a proximal end a connecting structure 1 for connection to anot shown monitoring and/or controlling device such as a pacemaker, acardiac defibrillator device or the like, an intermediate flexible leadpart 2, and a so called header 3 in a distal end. The header is providedwith a helix 4, which can be screwed out in the axial direction of thelead from a cavity in the distal end of the header. The helix has thefunction of attaching the distal end of the lead to the heart, by beingscrewed into the tissue, and also functions as an electrode forreceiving and/or transmitting electrical signals from and to the tissue,respectively. The header is also provided with a second electrode, a socalled indifferent electrode 5, which is positioned a small distancefrom the distal end and has the purpose of forming a complete currentpath together with the helix. The helix 4 and the indifferent electrode5 are each electrically connected to a first and second connector 6, 6′,respectively, in form of electric contact surfaces at the connectingstructure 1 by means of electric conductors within the lead. In FIG. 1the helix is illustrated in an extended state, whereas the helix isretracted into the cavity of the header in FIG. 2. The retracted stateis assumed during insertion of the lead to the intended position insidea human or animal body and once the distal end has reached the intendedposition of implantation, the helix is screwed out from the header andinto the tissue for attaching the lead to an organ.

Next, reference is made to FIGS. 3-6, in which is illustrated a firstembodiment of the invention in longitudinal sections, in FIGS. 3-5,through the distal end of the lead and in a perspective view in FIG. 6.As is commonly known in the art, the helix 4 is attached to anelectrically conducting shaft 7, which is rotatable and displaceablewithin the header 3. In a proximal end, the shaft 7 is connected to atorque transferring member, which in the illustrated embodiment alsofunction as conductor since it is formed as a wire coil 8 composed of atleast one electrically conducting wire and can be rotated by rotating acontrol pin 9 (FIG. 1) in the proximal end of the lead. The wire coil 8connects the helix to the first connector 6 on the control pin 9. Inaddition to the inner wire coil 8, the lead also comprises a second,outer wire coil 10, which connects the indifferent electrode 5 to thesecond connector 6′. The helix is journal led in a helicoidal groove 11on the inside of the header. Accordingly, when rotating the shaft 7 bymeans of the inner wire coil 8, and hence also the helix 4, the shaftand the helix will be extended from the retracted position illustratedin FIG. 3, which position is maintained during insertion of the leadinto a body, e.g. through a vein or the like, to the fully extendedposition illustrated in FIGS. 4 and 5. Since the helix is electricallyconducting and will function as an electrode, it is important that an aslarge part as possible of the helix is screwed into and embedded withinthe tissue 12 of a heart, as is illustrated in FIG. 5. However, althoughthe helix is fully screwed out from the header, a situation asillustrated in FIG. 4 could occur, i.e. the helix 4 is fully screwed outbut only a part of the helix is screwed into the heart tissue 12 and thedistal end of the header 3 is positioned with a distance from the tissuesurface. This situation has the disadvantage that the electric contactbetween the helix and the tissue is reduced and also that the mechanicalattachment of the lead to the tissue will be poor such that there is arisk that the lead could be accidentally detached from the tissue duringuse. Moreover, this situation is hard and many times even impossible todetect for a physician performing the implantation. It is often possibleto ensure that the helix is fully screwed out from the header but, sincethe tissue is invisible on traditional x-ray imaging and the mechanicalattachment could withstand a traditional pulling test, it is in priorart not possible to detect whether the helix is satisfactory screwedinto the tissue or not.

For this reason, the medical implantable lead is provided, in additionto a first electric contact surface on the helix, with an additionalelectric contact surface on a distance from the tip of the helix, whichin the embodiment according to FIGS. 3-6 is formed as a pin 13positioned centrally on the distal surface of the shaft. The pin is inelectric contact with the shaft 7, i.e. has the same electric potentialas the helix. By means of the pin it is thus possible to detect whetherthe helix is screwed into the tissue to such an extent that also the pinis in electric contact with the tissue or not. However, in order toallow such a detection, it is necessary that the helix is not electricconducting at that moment. For this reason the helix in this embodimentis coated with a biologically dissolvable layer 14, which during and ashort period after implantation will insulate the helix electricallyfrom the tissue. During this helix insulating period it is possible todetect by means of some kind of electric measuring device, when the pin7 will come into electric contact with the tissue 12 and then there isno doubt that the helix is screwed sufficient far into the tissue. Whenthe medical implantable lead has been implanted in the body for asuitable time period, the electrical insulating layer 14 over the helix4 will be dissolved and the helix can start functioning as an electrodein the tissue. The length of the time period during which the electricinsulating layer is effective may be altered by selecting differentmaterials by which the electric insulating layer is composed of and thethickness of the layer.

In FIG. 7 is disclosed a second embodiment of the invention which issimilar to the embodiment according to FIGS. 3-6. However, in thisembodiment the shaft 7 is not provided with a pin. Instead the distalend of the shaft is formed with a planar contact surface 15 which, whenthe helix is correct mounted, will abut against and make electriccontact with the surface of the tissue, which is detectable by means ofan electric measuring device. As in the embodiment according to FIGS.3-6, the helix is coated by an electrically insulating layer 14 of abiologically dissolvable material.

FIG. 8 illustrates a third embodiment by which the shaft is not providedwith an auxiliary contact surface, like the pin and the planar contactsurface of the first and second embodiments according to FIGS. 3-6 and7, respectively. Like these embodiments, the helix 4 is coated with anelectrically insulating layer 14 of a biologically dissolvable material.However, in this embodiment only a distal portion of the helix is coatedwith an electrically insulating layer, whereas the most proximal portion16 of the helix a short distance beyond the distal end of the header hasno insulating layer but is electrically conducting already at the pointof time for implantation. Accordingly, if the lead is correctlyimplanted the physician performing the implantation may get anindication of this by measurement by means of an electric measuringdevice since the proximal portion 16 of the helix having no electricallyinsulating layer will be in electric contact with the tissue. On thecontrary, if the lead is incorrectly implanted such that only the distalportion of the helix having an electrically insulating layer 14 isscrewed into the tissue, the physician can detect this since there willbe no electrical connection between the helix and the tissue uponmeasurement.

A fourth embodiment of the invention is illustrated in FIG. 9. Here, thehelix has no electrically insulating layer of a biologically dissolvablematerial, as in the previous embodiments. Instead, the shaft 7 isprovided with a pin 13 in its distal end which is electrically insulatedfrom the shaft. A separate insulated conductor 17 is arranged in acentral passage in the longitudinal direction of the shaft between thepin and an electrically controlled switch 18 in the proximal end of thehaft. The switch 18 can for example be arranged as any of the switchesin U.S. Pat. No. 5,423,873 or U.S. 2008/0294218. By arranging a switchof this kind it is possible to have one conductor, the inner wire coil 8between the proximal end of the lead and the switch, and by controlsignals control the switch to connect either to the pin 13 or to thehelix 4. By switching to the pin during implantation it is possible tomeasure if the lead is correctly mounted, in which case there will be anelectric contact between the pin and the tissue. When it is confirmedthat the implantation is properly performed, the switch is connected tothe helix to activate the helix as an electrode inside the tissue.

A fifth embodiment illustrated in FIGS. 10 and 11 is similar to theembodiment in FIG. 9 in that it comprises a switch 19 connecting aconductor 8 between the proximal end of the lead and the switchalternately to the pin 13 or the helix 4. However, in this case theswitch is mechanically operated by means of a stylet 20, which can beinserted into an open bore from the proximal end of the lead to theswitch. As can be seen from the enlarged longitudinal section of theswitch in FIG. 11, it comprises an electrically conducting displaceablemember 21, which is accommodated in a sliding manner inside anelectrically insulating tubular member 22 and which assumes an initialposition according to FIG. 11 by action of a spring 23. The displaceablemember 21 is connected to a conductor in the inner coil 8 in a not inthe drawings shown way. In the initial position according to FIG. 11,the displaceable member 21 is in electric contact with a first contactmember 24 on the inside the tubular member. The first contact member isconnected to the helix via the shaft 7 and a wire 25. Also a secondcontact member 26 is arranged on the inside of the tubular member whichis connected to the pin via the insulated conductor 17 inside the shaft7 and a wire 27. At the time for implantation of the lead it is possiblefor the physician to 7 operate the displaceable member 21 by pushing thedisplaceable member to a second position (not illustrated) by means of astylet 20 where it comes into contact with the second contact member 26.With the displaceable member in the second position it is possible tomeasure whether the pin 13 is in contact with the tissue or not and assoon as the pressure on the displaceable member from the stylet 20 isreleased, the displaceable member will return to the initial positionand the helix 4 will be connected to the first connector 6 in theproximal end via the conductor in the inner wire coil 8 and willaccordingly function as an electrode.

FIG. 12 illustrates a sixth embodiment of the invention. This embodimentis similar to the fourth and fifth embodiments according to FIG. 9 andFIGS. 10-11, respectively. However, it is not provided with any switchin the proximal end of the shaft. Instead, the insulated conductor 17within the center of the shaft 7, leading from the pin 13, is connectedto a contacting member in the proximal end of the shaft. By means of anelectrically conducting stylet 29, preferably having a surroundingelectrical insulation 30, an electric measuring device at the proximalend of the lead can be brought into electric contact with the pin suchthat a physician may detect whether the pin is in electric contact withthe tissue or not and accordingly whether the helix is screwedsufficient far into the tissue.

Also in a seventh embodiment according to FIG. 13, the pin 13 isconnected to an insulated conductor 17 in the center of the shaft 7.However, in this embodiment, the insulated conductor is connected to aseparate insulated wire 31 in the inner wire coil 8, whereas the helix 4is connected to another separate insulated wire 32 in the same innerwire coil 8. The wire to the pin and the wire to the helix are moreoverconnected to separate connectors at the connecting structure in theproximal end of the lead (not shown in the drawings). In this way it ispossible to connect the pin to a measuring device to detect whether thepin is in electric contact with the tissue or not. When it is assuredthat the helix is correctly mounted to the tissue, the helix can beconnected to the pacemaker or cardiac defibrillating device byconnecting it to the corresponding connector.

An eighth embodiment of the invention is illustrated in a schematiclongitudinal section of the distal end of the shaft 7 and the proximalend of the helix 4 in FIG. 14. In this embodiment the lead is providedwith, in addition to an internal through bore from the proximal end tothe proximal end of the shaft, also an internal through bore 33 throughthe shaft. An electrically conducting stylet 34 is inserted into thethrough bore from the proximal end of the lead such that a tip 35 of thestylet projects from the distal end of the shaft. According to thisembodiment, the stylet 34 can be inserted into the through bore when thedistal end of the lead is attached to the heart tissue by means of ahelix 4 at a desired position. The tip 35 of the stylet will thenfunction as the second contact surface, the body of the stylet as anelectric conductor and the proximal end of the stylet as a connector.Accordingly, by connecting an electric measuring device to the proximalend of the stylet, it can be established whether the tip is in contactwith the tissue or not. If it is established that the tip is in contactwith the tissue, this is an indication that the helix 4 is properlyattached to the tissue. Otherwise the helix is not properly attached. Inorder to restrict the projection of the stylet from the distal end ofthe shaft, and accordingly prevent too deep penetration of the styletinto the tissue, it is provided with a stop member in form of a shoulderportion 36, which goes into engagement with a stop member in form of ashoulder portion 37 on the inside of the through bore 33 of the shaft 7.To prevent electric contact of the stylet with the shaft and with thewire coil (8) inside the lead, the stylet is coated with an electricallyinsulating layer over its entire length except for the tip 35 and theconnector surface in its proximal end.

What is claimed is:
 1. A medical implantable lead adapted to beimplanted into a human or animal body to monitor and/or control an organinside the body, the lead comprising: an intermediate flexible leadpart; a connector at a proximal portion of the intermediate flexiblelead part; a tubular header at a distal portion of the intermediateflexible lead part; a rotatable shaft disposed within the tubularheader, wherein the rotatable shaft is extendably and retractablyarranged relative to the tubular head; an electric conductorelectrically coupling the connector to the rotatable shaft; a helix at adistal end of the rotatable shaft, wherein the helix is electricallycoupled to the rotatable shaft, and wherein the helix is configured forfixation to the organ upon rotation and extension of the rotatableshaft; and a pin at a distal end of the rotatable shaft, wherein the pinis electrically coupled to the rotatable shaft and is electricallycoupled to the helix, and wherein the pin is configured for electricalcontact to the organ upon rotation and extension of the rotatable shaft;wherein the pin, the rotatable shaft and the helix are arranged in aunipolar configuration; wherein prior to implantation of the lead, thehelix having a first configuration comprising an electrically activesurface coated with an electrically insulative layer of a biologicallydissolvable material to render the helix electrically inactive; whereinupon fixation of the helix into the organ, the helix having the firstconfiguration and the pin being in electrical contact with the organ todetect proper fixation of the helix into the organ; and whereinsubsequent to fixation of the helix into the organ, the helix having asecond configuration comprising the electrically active surface exposedupon dissolving of electrically insulative layer of the biologicallydissolvable material to render the helix electrically active.
 2. Themedical implantable lead of claim 1, wherein the pin is coaxiallyarranged in relation to the helix and projects distally from the distalend of the rotatable shaft.
 3. The medical implantable lead of claim 1,wherein the pin is separate from the helix.
 4. The medical implantablelead of claim 1, wherein the pin is adapted to penetrate into tissue ofthe organ.
 5. The medical implantable lead of claim 1, wherein alongitudinal length of the pin is less or equal to half a longitudinallength of the helix.
 6. The medical implantable lead of claim 1, whereinthe pin is adapted to penetrate into the tissue.
 7. The medicalimplantable lead of claim 1, wherein the pin has a same electricpotential as the helix.
 8. The medical implantable lead of claim 1,wherein the pin is disposed centrally on the distal end of the rotatableshaft.